The long-term goal of this proposal is to define the role of Hsal2 in myelopoiesis. Hsal2 is a recently identified divergent homeobox gene that has sequence homology to the Sal homeobox gene in Drosophila. Mutations of Hsal family member lead to Townes-Brockes syndrome with multiple organ developmental defects. Hsal2 expression is present in most human tissues including hematopoietic tissues. Several lines of evidence suggest that Hsal2 may be involved in myelopoiesis: (1) The transcriptional regulation of Hsal2 is controlled by two independent promoters and both promoters bear multiple putative binding sites for regulatory genes critical for myelopoiesis, including Wilms' tumor suppression gene (WT 1) and retinoic acid receptor-c_ (RAR); (2) WT 1 represses both Hsal2 promoter activities while retinoic acid (RA) activates Hsal2 expression in a luciferase reporter gene system; (3) Hsal2 expression coincides with the myeloid lineage commitment; (4) The myeloid population in Hsal2-null mice is significant reduced. Therefore, I hypothesize that an intracellular WT 1/RAR-a/Hsal2 pathway may play a role in normal hematopoiesis. The biological function of Hsal2 in myelopoiesis will be studied by overexpression of Hsal2 isoforms in hematopoietic stem cells, myeloid cell lines, and tetracycline-inducible embryonic stem cells in vitro, and characterization of Hsal2-null mice in vivo. We will continue to characterize the transcriptional regulation of Hsal2 with a focus on identification of the binding sites of WT1 and RAR-m The antagonistic effect between WT1 and RAR-_t on Hsal2 expression will be further explored by overexpression of WT1 in myeloid cell lines. The knowledge gained by these studies will contribute to better understanding of pathways critical for normal hematopoiesis and help to develop novel strategies to combat leukemia. The principal investigator, Dr. Li Chai will conduct the laboratory research under the guidance of a sponsor, Dr. Diane Krause, and an advisory committee. In addition, a further objective of this proposal is to serve as a vehicle for the development of the candidate into an independent and productive investigator in the area of hematopoiesis and leukemogenesis.